1. Field of The Invention
The invention relates to a radiation-emitting semiconductor diode, in particular a laser (amplifier) diode, comprising a semiconductor body with a semiconductor substrate of a first conductivity type on which a semiconductor layer structure is present which comprises in that order a first cladding layer of InP and of the first conductivity type, an active layer, a second cladding layer of InP and of a second conductivity type opposed to the first, and at least one separate confinement layer situated between the active layer and the first or second cladding layer, while the substrate and the second cladding layer are provided with electrical connections such that, given a sufficient current strength in the forward direction across a pn junction formed between the first and the second cladding layer and within a strip-shaped active region of the active layer, radiation can be generated whose wavelength is greater than or equal to 1 .mu.m, and in which semiconductor body a strip-shaped region is present which comprises at least the second cladding layer, the separate confinement layer, and the active layer and which is bounded on either side by a third cladding layer of InP. The invention also relates to a method of manufacturing such a diode.
Such a diode is used inter alia as a transmitter or amplifier in systems for optical glass fiber communication. In that case the emission/amplification wavelength often lies between 1.3 and 1.6 .mu.m.
2. Description of The Related Art
Such a diode is known from "Novel etching technique for a buried heterostructure GalnAs/AlGalnAs quantum-well laser diode" by A. Kasukawa et al., published in Appl. Phys. Lett. 59(11), Sep. 9, 1991, pp. 1269-1271. This relates to a so-called SIPBH (Semi-Insulating Planar Buried Hetero) diode with InP cladding layers and an active layer of GaInAs/AlGaInAs on an InP substrate. A strip-shaped region of the diode here comprises the upper cladding layer, the active layer, and two separate confinement layers adjoining the latter. The strip-shaped region is bounded on either side by an InP current-blocking layer. The active layer has an MQW (=Multi Quantum Well) structure. The separate confinement layers comprise a GRIN (=GRaded INdex) portion which is 0.1 .mu.m thick and comprises AlGaInAs of which the aluminum content shows a gradient from 20% to 38%, and a 0.1 .mu.m thick portion which comprises AlGaInAs with an aluminum content of 38%. Such a diode of the buried hetero type has particularly attractive properties such as a low starting current, a stable lateral modus, a substantially circular-symmetrical radiation beam, and a low parasitic capacitance. The use of GalnAs(P)/AlGaInAs for the active layer has the important advantage over the alternative GaInAs(P)/GaInAsP that the jump in the conduction band is much greater, which gives the diode a particularly high efficiency and a low starting current, while the latter quantity in addition increases little with an increase in temperature.
A disadvantage of the known diode is that its starting current rises comparatively strongly in time. This renders the diode unsuitable for use in an optical communication system because a useful life of, for example, 20 to 25 years is required for this, whereas the known diode shows an inadmissible increase in the starting current after 500 to 1,000 hours already.